The Grapevine

DNA Structure Of Hemp And Marijuana Far More Different From One Another Than Previously Thought

Cannabis
Scientists conduct the first large-scale genetic study of hemp and marijuana and find plenty of surprises waiting for them. James St. John, CC BY 2.0

It’s the sort of question that stoners, hemp farmers, and scientists alike have pondered for thousands of years: Just what exactly is cannabis made out of? Now, thanks to the authors of a PLOS-One study published Wednesday, we may have a much clearer answer.

The Canadian researchers unraveled the genetic structure of 81 different marijuana and 43 hemp samples, in an attempt to test long-held assumptions about the diverse plant. They found that the differences between hemp and marijuana run far deeper than the level of tetrahydrocannabinol (THC) present in them, and that the advertised ancestry of many commercial strains of marijuana is often times misleading.

Though the cannabis plant can be broadly broken down into three species, C. sativa, C. indica and C. ruderalis (C. ruderalis being the most controversial distinction), there are canyon-sized gaps in the classification of marijuana and hemp. Commercial marijuana is divided into exotically named, but hardly scientifically validated, strains, while hemp is defined by its low THC content in comparison to marijuana — THC being the main psychoactive component in cannabis — and is classified into different cultivars.

“The classification of Cannabis populations is confounded by many cultural factors, and tracing the history of a plant that has seen wide geographic dispersal and artificial selection by humans over thousands of years has proven difficult,” the authors wrote.

One of these long-standing cultural factors has included the plant’s illegality in various parts of the world, including even Canada, which only legalizes marijuana for medical use. "Even though hemp and marijuana are important crops, knowledge about cannabis is lacking because of its status as a controlled drug," said study author Dr. Jonathan Page, a botanist at the University of British Columbia, in a statement.

Despite these legal hurdles, the research team was able to procure enough varying samples that they were able to compare their genetic structures to one another and to the ancestral lineage of C. sativa and C. indica plants.

While hemp cultivars are largely considered to be derived from C. sativa, the authors were surprised to find out that nearly all their samples were genetically more related to the C. indica species. The genetic differences between hemp and marijuana also accounted for more than simply the level of THC each type of plant could produce, though the authors were quick to note that “hemp and marijuana still largely share a common pool of genetic variation.”

As for the commercial strains, which are often defined by their relationship to either C. indica or C. sativa, the authors only found a moderate association between the reported ancestry of the strain and its actual genetic history (like dogs, marijuana strains are often a mix between the two). In one particular case, the Jamaican Lambs Bread strain, advertised as entirely belonging to the C.sativa species, was found to be nearly genetically identical to a C.indica strain from Afghanistan.

"Cannabis breeders and growers often indicate the percentage of Sativa or Indica in a cannabis strain, but they are not very accurate," Page said.

The largest study of its kind, the authors are hopeful that their findings can highlight the need for a better system of marijuana classification, though they acknowledge its inherent difficulty.

“Achieving a practical, accurate and reliable classification system for Cannabis, including a variety registration system for marijuana-type plants, will require significant scientific investment and a legal framework that accepts both licit and illicit forms of this plant,” the authors concluded. “Such a system is essential in order to realize the enormous potential of Cannabis as a multi-use crop (hemp) and as a medicinal plant (marijuana).”

Source: Sawler J, Stout J, Gardner, K, et al. The Genetic Structure of Marijuana and Hemp. PLOS-One. 2015.

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